ABSTRACT The developmental stage of the brain at the stroke onset plays key role in injury. Inflammation is a hallmark of perinatal brain injury, both early injury and repair. Previous therapeutic efforts were mostly focused on protecting neurons acutely, but such strategies appeared to be short-range. Very few studies focused on the development of agents that target cerebrovascular interface. Our long-term goal is to identify effective and safe therapy for perinatal stroke and facilitate translation into clinical practice. Emerging evidence in human infants has suggested that n3-Polyunsaturated Fatty Acids (n3-PUFA, i.e., Omega-3 fatty acids and derivatives/metabolites) play an important role in both normal postnatal brain development and in injured newborn brain. In rodents, n3-PUFA are shown protective in adult stroke, in juvenile brain after infection and in neonatal brain after neonatal hypoxia-ischemia, affecting an array of individual inflammatory mechanisms and vascular effects. We propose to identify whether n3-PUFA exert beneficial effects after perinatal stroke by a central mechanism?by attenuating sphingosine-1-phosphate (S1P)/S1P receptor 2 (S1PR2)- mediated signaling at the immune-neurovascular axis and reorganizing lipid signaling. Enhanced mechanistic understanding of n3-PUFA-mediated effects in reducing injury and/or facilitating brain repair in newborns who suffer perinatal stroke would allow for almost immediate changes in management of injured newborns to enhance their brain development and long-term motor and cognitive outcomes. Demonstration that S1P/S1PR2 signaling is the target n3-PUFA will lead to identification of new therapeutic targets for perinatal stroke. We will test the central hypothesis that n3-PUFA enhance brain repair after perinatal stroke by modifying S1P/S1PR2 signaling at the immune-neurovascular axis. In Aim 1, we will determine effects of dietary n3-PUFA in attenuating neuroinflammation and vascular inflammation after perinatal focal arterial stroke or infection, and in microvessels isolated from acutely injured neonatal brain in mice with intact or disrupted S1PR2 signaling. In Aim 2, we will examine long-term effects of dietary n3-PUFA, and of altered brain lipid composition, on brain repair, brain connectivity and functional outcomes after perinatal focal arterial stroke. In Aim 3, we will examine short-term and long-term effects of post-stroke pharmacologic S1PR2 inhibition and n3-PUFA administration on vascular remodeling, brain connectivity and improved functional performance. We will use a novel clinically relevant perinatal focal arterial stroke model that we invented, in conjunction with loss-of-function and gain-of function genetic and pharmacological approaches and advanced non- invasive imaging methodologies, to understand how to target immune-neurovascular axis to enhance brain repair after perinatal stroke. Novel approaches to examine vascular inflammation and create atlas of the remodeling vasculature and of vessel-microglial interactions in vivo over time, together with brain connectivity measures, will enhance the understanding of brain repair in the disease.